Understanding the precision and mechanism of Servo Motors


Servo motors are a remarkable type of motor known for their exceptional precision in rotational movement. These motors consist of a control circuit that plays a vital role in maintaining accurate positioning of the motor shaft. The feedback provided by this control circuit allows servo motors to achieve unparalleled precision in their rotation. Applying a servo motor becomes essential if the task involves rotating an object with specific angles or distances. The foundation of this technology lies in a straightforward motor, cleverly integrated with a servo mechanism.

DC and AC Servo Motors

Servo motors can be categorized into two primary types based on their power source: DC and AC. A servo motor is classified as a DC servo motor if it operates with a DC power supply, while the term AC servo motor is reserved for those powered by an AC source. In this discussion, we’ll focus on the working principles of DC servo motors. Beyond these fundamental divisions exist various servo motor subcategories that vary based on gear arrangements and operational characteristics.

Unveiling the Mechanics of a Servo Motor

A distinctive feature of servo motors is the incorporation of a gear arrangement, which facilitates high torque delivery despite their compact and lightweight design. This unique attribute positions them as crucial components in diverse applications such as toy cars, remote-controlled helicopters and planes, and robotics.

Servo motors are typically rated in kg/cm (kilograms per centimeter), with hobby servo motors commonly rated at 3kg/cm, 6kg/cm, or 12kg/cm. This rating denotes the weight a servo motor can lift at a specific distance from its shaft. For example, a 6kg/cm servo motor can lift 6 kilograms when the load is suspended 1cm away from the motor’s shaft. The carrying capacity diminishes as the distance from the shaft increases. Electrical pulses influence the servo motor’s positioning, and its circuitry is adjacent to the motor.

Inner Workings of the Servo Motor

A servo motor comprises three key components: the controlled device, the output sensor, and the feedback system. This arrangement operates as a closed-loop system, utilizing positive feedback to regulate motion and the final position of the motor’s shaft. A feedback signal compares output and reference input signals to steer the device’s behavior.

The reference input signal is matched against the reference output signal, leading to the feedback system’s generation of a third signal. This third signal serves as input for controlling the device. As long as the feedback signal persists or a disparity between the reference input and output signals exists, this control signal remains active. The central role of servomechanism is maintaining the system’s output at the desired value despite external disturbances.

Servo Motor’s Operating Principle

The fundamental components of a servo motor include a motor (DC or AC), a potentiometer, a gear assembly, and a controlling circuit. To start, the gear assembly reduces the motor’s revolutions per minute (RPM) while amplifying its torque. In its initial position, the potentiometer’s output signal remains absent due to its configuration.

An electrical signal is then fed to one of the error detector amplifier’s input terminals. The ensuing difference between the potentiometer-generated signal and signals from other sources undergoes feedback processing, resulting in an error signal. This error signal becomes the motor’s input, initiating its rotation. The motor’s shaft is linked to the potentiometer, ensuring that as the motor turns, the potentiometer generates a signal. Consequently, the angular position of the potentiometer drives changes in its feedback signal.

After a period, the potentiometer aligns itself to produce an output matching the external signal. This equilibrium halts the amplifier’s output to the motor, as no difference remains between the external signal and the potentiometer-generated signal. This cessation leads to the motor’s halt.

Mastering Angular Precision: PWM and Servo Motors

Servo motors are controlled through pulse width modulation (PWM). This entails regulating the rotation angle by manipulating the pulse duration applied to the motor’s control pin. Comprising a DC motor managed by a variable resistor (potentiometer) and gears, servo motors harness high-speed force to generate torque. The interplay of force and distance manifests as a higher force and shorter distance in servos than in DC motors.

The potentiometer, integrated with the servo’s output shaft, calculates the angle and orchestrates the DC motor’s halt at the intended angle. Servo motors can rotate from 0 to 180 degrees, potentially extending to 210 degrees based on the manufacturer’s specifications. This range is modulated through appropriately timed electrical pulses. With pulse widths of 1 ms, 1.5 ms, and 2 ms, servo motors can be positioned at 0, 90 (neutral position), and 180 degrees, respectively, demonstrating the precision of their control.

Power and Planning: Servo Motor Management

Servo motors conventionally function within a +5V supply range. However, carefully considering their current consumption is crucial if implementing more than two servo motors. Integrating a proper servo shield is recommended to manage this effectively, ensuring optimal performance and preventing potential issues arising from excessive power demands.

In conclusion, servo motors are a testament to precision engineering, enabling accurate rotational movements through sophisticated control mechanisms. From their classifications based on power sources to their intricate internal workings, servo motors propel innovation across various industries, underscoring their indispensability in modern technology.